when i try to update my system it will not connect to the app store. says there is no internet connection...

If one of the last updates performed was the beta version 10.13.4 there

may (or not) be something of a co-incidental happening going on...

Your system profile and logs should show the existence of internet access;

then to check each of them over again. Plus restart; perhaps in Safe mode.

•Use safe mode to isolate issues with your Mac - Apple Support

Not sure how to suggest you troubleshoot, but that's what may be necessary.

There also are other system re-sets and partial bits of information in their site

pages to try & see if they help. In SMC, before that reset is used, try the others.

Where it says Before you reset the SMC: try each of those, then restart & test:

How to reset the System Management Controller (SMC) on your Mac - Apple Support

Some odd quirks may be flushed out by resetting NVRAM but don't expect magic.

Good luck & happy trails! 🙂

Apps like Little Snitch and anti-virus software can interfere with the iTunes/App Store connections.

ASC - Late 2012 Mac mini, macOS 10.13.3;  Watch, 38 mm AL, watchOS 4.2.2; iPad Air 2 & iPhone 7+, iOS 11.2.5; TV 4th Gen, tvOS 10.2.5;  Airport Express.